Mineral-tanned leather and method of making the same



' being to provide means ,those of metals closely related to iron and Patented Feb. 1, 1927.

FRIEDRICH W. WEBER, OF. H ACKENSACK, NEW JERSEY mnnnar-rannnn LEATHER AND METHOD or MAKING 'rnn SAME.

No Drawing.

This invention relates to leather and -it particularly relates to leather tanned with metal oxides of the general type Me O preferably such as iron oxide, chromium oxide and the like and with the oxides of the rare earth metals, or compounds, very poor in acid,of the same, the object of the invention by which a leather of superior qualities can be obtained at a low price and in a short time.

The tanning properties of iron oxide have been known for several centuries but the difiieulty to find a proper solution of this oxide allowing its convenient application in the tanning process was too great as to favor a development of the iron tanning process notwithstanding the well-known efforts by Knapp and his many successors. I

The difliculties in the application of the salts of the various metals are surprisingly solved and the tanning greatly simplified by my new invention of combining the tanning effected by iron and chromium salts and chromium, with my new tanning method of applying the salts'of the rareearth. metals as described in my cop'ending patent application, entitled Treating animal tissue, filed under Serial No. 704,282. The metals of the iron group are preferably applied in.

' tanning ath as basic ferric acetate and only in the form of theirchlo rides or sulfates, their application depending to a large extent on the price as to which gives the greatest economic advantages.

My new invention is based on the saturation of pickled hides with a solution of basic acetates of the rare earth metals before they come in touch with a.tanning solution consisting ofone of the salts of the metals referred to above, for instance with my new colloidal ferric chloride solution made as described below, and to dry the hides thus satmy new process -urated. During this drying process acetic acid is split off and vaporized causing a deposition of oxides of the rare earth metals,

or of more basic compounds of the same which are very poor in acid, Within the hide whereby a leather is obtained similar to that furnished by tanning with alum and salt, but 50 having a greater quantity of metal oxide in view of the higher atomic weight of the rare earth metals. be dried hides, or leather,

are returned to the same bath of basic ace-' rates of the rare earth metals, the bath having'a content of sodium chloride correspond-' Ting to 5 B.-and.con-taining for each liter Application filed March 19, 1925. Serial No. 16,860.

.of its volume 100 cc. of a saturated solution of acetates of the rare'earth metals.

To this bath I now add the colloidal basic ferric chloride solution referred to above. Adding this ferric chloride solution causes no precipitation whatever, ,on*the contrary the tanning process sets in immediately, thin hides being tanned in about two hours, while thicker ones require a correspondingly longer time. The tanning e'flt'ect produced hereby is so perfect that the. hides can be removed immediately from the tanning bath to the drying chamber and illtimately, when dry, show no shrinking whatever, nor are there any hard spots, nor any rubberlike swelling, they can immediately be worked mechanically by stretching and stale ing. If these leathers are soaked in water their content-of sodium chloride is leached out as well as a very minute quantity of rare earth metals, but not a trace of iron.

The unwashed, dried hide,'or leather, is then treated in a substantially neutral soap solution at a temperature of 4t0-50 C., dried a little sodium carbonate needs to be added to the supernatant, almost colorless solution to quantitatively precipitate the carbonates of the rare earth metals, free of iron, the filtrate from the carbonates containing all sodium chloride and a little acetate. This sodium chloride solution will probably have a concentration of 5 B. as very little dilution takes place during the tanning process, otherwise itcan 'be adjusted to this concentration and be used over again in the tanning process.

VVhy itis possible that "a good tanning effect can be obtained with the process with' out a premature precipitation of the iron liquor, appears to be explained by my ob servation that the presence of the basic acetates of the rare earth metals precipilate the iron oxide only very gradually and that upon the addition of this iron liquor to r which gradually turns. smoky so slowly than sodium chloride can be applied without any v Fe Cl, solution.

To 200 cc. of this solution are added preferably 25 grams of a 57 mixture of car- I bonates of the rare earth metals (computed on oxide) which must not necessarily be absolutely free of. phosphate, or sulfate, and wlth a copiousfdischarge of gases according to the equations 1. 2racu+ m, co,),+6n,o-

in which Fe-stands as representative of any metal of the iron group formin oxides of the general type Me. .-O and lanthanum, the

' carbonate of which can be safely considered of the rare earth metals, a dark-red, trans-' constituted as stated above, represents any parent and clear solution is obtained; it thickens within a few hours into a rather viscous syrup which dissolves .in water in every proportion and even on boiling stays clear; it may turn smoky at continued heating, but the solution always clears again on cooling. If one adds, however a single kernel of sodium sulfate to the clear solution either before or after boiling, immediately a heavy precipitation of' ferric hydrate takesplace while the rare earth metals stay dissolved.

This efl'ect of the sodium sulfate causes a coagulation, or precipitation, of ferricoxyhydrate; if this precipitate happens the 4 ution always turns more acid the more ferric-oxyhydrate is precipitated; this acid, however, cannot do any harm to the hides, nor will it redissolve the ferric-oxyhydrate precipitated in the hide about to be tanned; it is obvious that the salts of the rare earth metals, still present in the tanning liquor, then continue the tanning process and cover the iron already deposited in the leather.

To facilitate the understanding of my invention I shall describe by way of example how I proceed to carry the same into effect:

Dry calf hides for instance, which were previously ickled in the usual bath-containing 1% sulp uric acid and 5% sodium chloride are soaked in a sodium chloride solution of 5B. until they are thoroughly penetrated and free of folds'and show a uniform apearance. As soon as this stage is reached add to this bath for each liter of its volume 100" cc. of a saturated solution of basic acetates of the rare earth metals which may be bought in the market in the form of a In this sodium chloride acetate soluwell fixed upon the hides, but they should not be dried too much so as to assume a great stiffness. ,The hides are then returned to the same bath to which I then add all at once 50 cc. of above colloidal ferric chloride solution, deacidified as explained above with the carbonates of the rare earth metals, for each 1 liter of bath liquor, without causing a precipitation in the solution even in the presence of sodium chloride and without swelling the hides, an excellent tanning efl'ect takes place immediately. As soon as this tanning process has proceeded so far that the hides are tanned also at their thick parts, the hides are taken out of the bath, drained off the excess of liquor and then dried which does not require the usual nailing as they will not shrink and reduce in their surface, nor will they get horny during the drying .process.

It is noteworthy that the unwashed dry leather obtained by my new process does not show the dangerous efllorescence of sodium chloride so often noticed in the products of,

From

other mineral tanning processes. practical considerations it appears desirable to dry with the sodium chloride in the leather and to submit the same then to the soaping process without washing the leather previous to this soaping process, as the leather thereby gets denser and waterrepellent to a high degree.

Inasmuch as the leather was-first saturated in the tanning process with the basic acetates of a mixture of the rare earth metals, 7

the oxides of which are therefore fixed durin the drying process on the fibers of the hi es, and was subzequently treated with the collodial ferric choride solution containing simultaneously also the basic chlorides of the rare earth metals, the iron oxide, or any other oxide of the general Me O is fixed upon the fibers of the hides together with the oxides of the rare earth metals; it can "therefore safely be said in view of the foundation laid by the preliminary treatment of the hides with the acetates of 'the rare earth metals and the tanning actionby the basic chlorides of the rare earth metals simultaneously with the precipitation of the iron as ferric-oxyhydrate, that the iron oxide is thoroughly intermixed with the oxides of the rare earth metals and is encased bv the same owing to the deposit of the oxides of the rare earth metals after nearly all iron oxide has been precipitated out of the colloidal tanning liquor; Though the iron oxide as well as the oxides of the rare earth metals deposited in the leather are generally insolub e in water, their relation to the hidesubstance, during the very short time that the tanning process is going on, is such that at leazt part of all the varlous oxides enter into a reaction with any soap solution with which the treated hide may be brought into contact, thereby forming the respective soaps; whether this is due to the influence of hydroxyl-groups still resent. in the molecules of the oxides or ue to traces of acid having just segregated from the basic salts in the tanning process and still present in the hide-substance, is diflicult to say.

- organic acid, tration of acid cannot take place 1n the The obtained leather exhibits a pleasant light tan color which logically seems to be the result of the double tanning process by means of iron and the rare earth metals; it is free of the. dark-red color of the other so-called iron-leathers which excludes a dyeing with light shades.

' From the aforesaid description it is evident that the leather during the tanning process was never touched by sulfuric acid,

but only by tanning solutions of weak acid reaction, among them one with a volatile wherefore a dangerous concenfinished leather; moreover, the presence of the oxides of the rare earth metals prevents the ferricoxide from being reduced to ferrous oxide at the expense of the hide itself and causes, if traces ofhydrochloric acid should be split off, to have them immediately neutralized.

To the above statements that the tanning liquor 'of the acetates of the rare earth metals containing also the colloidal ferric chloride solution deacidified as described above with the carbonates of the rare earth metals after the precipitation and filtration of the basic iron acetate yields a clear solution and that the carbonates of the rare earth metals may be precipitated therefrom by sodium carbonate I wish to add that these regenerated carbonates are of much greater purity than they were when first applied, since the last traces of iron ofthe rare earth metals have been precipitated with the whole mass of iron; thisiron free solution of the regenerated earth metals may of course also be used over. again in the tanning process to save their precipitation as carbonates.

The well known difliculties-in the application' of chromium alum as a. tanning material are soon overcome by extending my new process also to thismaterial. I have now found a way of producing an excellent tanning solution by starting directly from chromium alum, and that the new tanning solution thus cellent power of penetrating the animal hide without reducing the hide in surface, but also tans it completely in a very short time. Moreover, the tanning liquor stays clear until the ta'nningprocess is finished and thus ofiers the possi ility to let the hide soak over night in the bath without any danger of forming undersirable spots, or that the hides swelil or take on too much acid, and thus the application of chromium alum is renderedpossible by my process, which I am going to describe below, thoughthe chromium alum contains only the same amount of chromium as the sodium bichromate (M. W. 300) which has only one obtained has notonly' an exnew and improved third of the molecular weight of that of the chromium alum.

For the better understanding of my new process I will give an'example of how I make my new tanning solution from chromium alum:

200 grams crystallized are dissolved in 500 gr. until a dark green solution this solution I add then a and 40 grams of carbonates (containing 57% oxides) of the rare earth metals, and with the discharge of gas not onlya reduction in the sulfuric acid content of the alum is obtained, but also a solution of a basic chromium sulfate and of basic-sulfates of the mixed rare earth metals. During this reaction some chromium oxyhydrate is precipitated together with some calcium sulfate as the carbonates of the rare earth metals are liable'to contain some lime, andalso iron. which accompanies the rare earth metals as well as the chromium alum. The solution thus obtained is diluted up to 1 liter, hereafter it is allowed to stand to settle and the clear solution is then ready for use( In the case of chrome tanning I recommend the application of the carbonates of the rare earth metals particularly for the deacidification of all alums suitable for tanwater and boiled is formed; to paste of water chromium alum ning. In explanation of this situation I beg to refer to the observation of many anthorities in the chemistry. of tanning, who

state that the well dissociated or green chromium solutions'display the greatest tanning effect. If now to chromium alum, which contains the potassium sulfate as unneces sary ballast, the carbonates of the rare earth metals are added for the purpose of new" tralizing the sulfuric acid as well as for the purpose of forming salts having tanning or sulfates of the same, which speaks for their great affinity to potassium or so.

' earth metals, and yet the tanning takes place so surprisingly quick; in this connection I want tomention that by washing the tanned hides only the mechanically adhering part of the tanning solutionis removed, whereas that part, which penetrates the hide, is hydrolyzed which explains that the hides, originally appearing green, immediately assume a lighter color and give off the acid when washed with water. The hides treated with this new tanning solution are finally washed with water until the turn neutral litmus paper faintly red an the water itself stays neutral. Now the hides can be soaped.

, This soaping process is carried out as follows: I prepare from a good neutral textile soap, which has 10% fixed alkali and 30% water and does not contain more than 0.1% free alkali, a 5% solution and work the hides therein at a temperature of substan tially 60 C. until they are thoroughly satu-' rated with soap solution and show a sufliciently neutral reaction. Owing to the formation of chromium-soap, covered with the practically absolutely insoluble soap of these rare earth metals, a very soft leather of velvet or cloth like feeling is obtained, which is dried and subsequently may be-fat liquored' as desired. I .want to emphasize that it is of advantage to introducethe Well Washed hides into the soap solution when still showing a slightly acid reaction for the reason that any soap, originally absolutely neutral, splits off some alkali which then meets in the leather with some traces of acid-and is thus easily neutralized.

By my efforts to overcome the above described shortcomings peculiar to the Schultz process I have found out that a solution, obtained in" the manufacture of rare earth metal'compounds, may be applied with great advantage.

When in the manufacture of thorium I. salts the chlorides of the rare earth metals.

obtained by fusing monaz'ite sand with alkali and dissolving the washed oxides in hydrochloric acid in a formfree of phosphates, are acted. upon with a solution of sodium thiosulfate with the intention to separate the thorium in the form of its thiosulfate, the solution of-the chlorides obtained after filtering off the thorium thiosulfate and the molecular stilfur,; contains a great excess of sodium thio'sulfatewhich' is necessary if the thorium is to be precipitated quantitatively. This chloride solution now contains the chlorides of the remaining rareearth metals with very little'iron and as it is'neutral, it is for various reasons-extremely suitable as a reduction bath for a two bath process. For the first it contains enough sodium thiosulfate to reduce all chromic acid, which was fixed-upon the hides in the first bath, and secondly it contains a sufficient quantity of the chlorides of the rare earth metals which immediately act uponv the hide impregnated with chromic acid as soon as it is introduced into the bath simultaneously with the reducing action of the thiosulfate generating basic chromium chloride which acts as a tanning agent and is supported in its action by the chlorides of the rare earth metals without the necessity of adding any great amount of acid, which is important because this fact reduces the precipitation of molecular sulfur very considerably; this molecular sulfur is furthermore covered b the oxides of the rare earth metals which protect it against further oxidation. The whole tanning process is complete, and the leather shows very seldom any swelling and has a better feeling than with the well known Schultz chrome tanning process; they are also more easily finished by any of the well known ways. I may say that empty spots, so often encountered in the Schultz process are avoided because the presence of the rare earth metals appears to avoid such spots even if sli 'ht bleeding should take placeas with the t chultz process. This does not exclude that in the reduction bath chlorides of the rare earth metals may be direct- 1y applied after a sufficient amount of thiosulfate has been added thereto.

It stands to reason that I do not restrict myself to chromium alum as a source for lot a tanning solution, but I just as well start I According to this patent I effect the reduction by acidulating the sodium bichromate solution and then adding asubstance liberating S0 for instance sodium bisulfite to the same; the solution of chromium sulfate obtained thereby may then be deacidified by the carbonates of the rare earth metals that the acid combines with/the same forming thereby basic sulfates of the rare earth metals. as already described above.

I have furthermore found that I may proceed in the following manner especially if it is intended to produce a chrome leather of velvet like, soft feeling which is especially characterized by a smooth grain side:

The hides are treated in a 5 B. sodium chloride solution, to which bath, while being agitated, for each liter of its volume 100 cc. of a basic acetate solution of the rare earth metals are added. In this mixture of solutions the hides are well agitated for about 3 hours, then they are taken out of the bath, drained off, and put up for drying over night, whereby the oxides of the rare earth metals are completely fixed upon the hides.

The hides thus'dried are then put'back into the same bath to which I addfor each liter of its volume 100 cc. of a neutral chromium solution, for instance of a chromium alum deacidified as described above. Here item be observed that the tanning solution does not only stay clear, but gradually turns violet because of the formation of the sulfates of the rare earth metals. The tanning of the hides Iprogresses continuously; after three hours they are taken out of the bath. This operation can also-be performed in one bath by addin to the sodium-chloride solu-' tion for each liter of its volume, according to the thickness of the hide, 25 cc. of a basic acetate solution of the rare earth metals and of a corresponding quantity of chromium alum deacidified as described above; eventually the sodium chloride may be subst'ituted by sodium. sulfate. procedure extends the time of the tanning 'process quite considerably, but I obtain a soft and white leather. Theleather may finally be washed and soaped which yields a snow-white and very durable leather.

In'order to obtain a chrome leather of light shade'I can modify aforesaid process in the following manner: I 'deacidify aluminum sulfate, or potassium alum, sodium alum or any other suitable alum salt in a concentrated solution; for instance I dissolve 190 grams potassium aluminum sulfate in 500 cc. of water and add thereto 40 gr. carbonates of the rare earth metals until at an'elevated temperaturea lasting precipitate is formed whereby iron hydrate calcium sulfate and other impurities of the rare earth metals are precipitated; I 1 liter and allow to stand to clarify; 100 cc. of the clear solution and 100 cc. of the neutralized chromium alum are then added to each liter of the bath volume and the hides then tanned therein to be subsequently washed and soaped. All the leathers thus obtained are of course fat liquored in any of the well known ways but inasmuch as these after treatments are not part of the real tanning process, this branch of the treatment" of leather is here not dwelled upon.

It is also possible to obtain special effects by treating the leather with egg-yolk and wheat-flour, but' also these methods are here notfurther referred to as it is my intention to demonstrate, by this description how-by th methods based upon'the application of th rare earth metals compounds the various processes of tanning, especially those by iron This modified I lactic acid with greater. advantage dilute the solution thus obtained to ing basic salts,

and chromium salts, and by salts of the metals more or less related to aforesaid metals, can be improved and simplified, as one always works with clear solutions of excellent tanning power as their basicity is just right and is governed by a very fortunate proportion between the high atomic Weight of the rare earth metals and the relatlvely low amount of acid, i. e. in other words 'the rare earth metals have in their salts, whether sulfates, or chlorides, com ared with the corresponding salts of Al, 1', Fe, Mn, etc. the lowest amount of acid in their molecule;

furthermore it is due to the insolubility of the soaps of the rare earth metals that the leather obtained by the above processes are full and of soft feeling. 1

In recent years the'lactic acid has been introduced into tanning; though lactic acid has proved as 'an' excellent material for the deliming of the hides, in the form of its alkalia metal; salts as a reducing agent; for if lactic acid comes into contact with hides impregnated with chromic acid, it isoxidized to formaldehyde-and acetic acid. I have found out that the lac tates of the rare earth metals may we'lLbe applied as a reducing agent in .a reduction bath, where the are transferred into the acetates thus 0 ering a way 'for'applying nirxilg purposes.

. hatIclaimis: 1. The method of tanning hides comprising soaking pickled hides in a so ium chloride solution, adding thereto the solution of a rare earth metal compound capable of forming basic salts, agitating the hides in for tan?- it could only be usedthe mixture of the aforesaid salt solutions,

dryin the hides thus treated, returning the dried liides to aforesaid mixtures of salt solutions, adding to said mixture a solution containing the reaction mixture of a salt of a metal, forming an oxide of the type Me O with a basic compound of the rare earth metals, and drying... the hides thus treated.

2. The method of tanning hides, comprising soaking pickled hides in a sodium chloride solution, adding thereto the solution of a rare earth metal compound capable of formagitating the hides in the mixture of the aforesaid salt solutions, dryin the hides thus treated, returning the dried hides to aforesaid mixtures of salt solutions, adding to said mixture the solution containing the reaction mixture of a salt of a metal, forming anoxide of the general type Me O with a carbonate of the rare earth metals, and drying the hides thus treated.

3. The method of tanning hides with metal salts, said method comprising acting upon a hide with a solution containing a reaction mixture of asalt of a metal, forming the hides thus treated, returning the .an oxide-of the type Me o with a basic compound of a rare earth metal.

4. The method of tanning, hides with metal 'salts, said method comprising acting upon a hide with a solution containing a reaction mixture. of a salt of a metal, forming an oxide of the type Me O with a carbonate of a rare earth metal. v 5. The method of tanning hides, co mprisin soaking the pickled hides in a sodium chloride solution, adding to aforesaid bath of sodium chloride the solution of a salt of the rare earth metals capable of forming basic salts, agitating the hides in the mixture of the aforesaid salt solutions, dr rie hides to the aforesaid mixture of salt solutions, adding to said mixture a solution containing the reaction mixture of a chromium alum with a basic compound of the rare earth metals,' and drying the hides thus treated.

6. The method of tanning hides, comprising soaking the pickled hides in a sodium chloride solution," adding to aforesaid solution of sodium chloride the solution of an acetate of one of the rare earth metals, agitatin the hides in the mixture of the aforesai two salt solutions, drying the hides thus treated, returning the dried hides to aforesaid mixture of salt solutions, adding to said mixture a solution containing the reaction mixture of a chromium alum with a basic compound of the rare earth metals,

- and dr ing the hides thus treated.

7. T e method of tanning hides, comprising 'soakin the pickled hides in a sodium chloride so ution, adding to aforesaid solution of sodium chloride the solution of basic acetates of the earth metals, agitating the hides thus treated in the mixture of aforesaid two salt solutions, dryin the hides thus treated, returning the dried hides to the aforesaid mixture, adding to said mixture a solution containin the reaction mixture of a chromium alum w1th a carbonate of the rare earth metals, and drying the hides thus treated.

8. The method of tanning hides, comprisin soaking the pickled hides in a sodium chloride solution, adding to aforesaid solution of sodium chloride the solution of an acetate of one of the rare earth metals, agitating the hides in the mixture of the aforesaid two solutions, drying the hides thus treated, returning the dried hides to the 'ing soaking the pickled hides in a sodium chloride solution, adding to aforesaid solution of sodium chloride the solution of basic acetates of the rare earth metals, agitating the hides thus treated in the mixture of multaneously a basic chromium salt, and

acting with the solution thus obtained upon the hides. v a

p 11. The method of tanning hides, comprising heating the solution of a chromium alum at substantially. its boiling'poin t untilj said solution turns green, adding to afore--' said solution a basic compound of the rare earth metals thereby forming basic sulfates of the rare earth metals and basic chromium sulfate, and acting with the solution thus obtained upon the hides. 1

12. The method of tanning hides, comprising heating the solution of a chromium alum at substantially its boiling point until said solution turns reen, adding to aforesaid solution the car onate of a rare earth metal thereby forming a basic sulfate of the rare earth metals, and acting with the solution thus obtained upon the hides.

and soaking the dry hides in a soap 13. The method of tanning hides, consist- I ing in acting upon a solution containing a salt containing aluminum sulfate with a carbonate of the rare earth inetals, combining the solution thus obtained with a solution obtained by acting upon chromium alum with a carbonate of the rare earth metals, adding the aforesaid combined solutions to a bath of sodium chloride, acting with the mixture of all three solutions upon the hides, washing the hides thus treated, and acting. upon the washed hides with a soap solution.

14. 'As a new article of manufacture, a double tanned leather having fixed upon its fibersa deposit of one of the oxides of the rare earth metals and upon aforesaid deposit another one consisting of a mixture of a chromium-oxide and of an oxide of a rare earth metal.

15. As anew article of manufacture, a double tanned leather having fixed upon its fibers a mixture of a metal oxide of the general type Me O and of an oxide of a rare earth metal.

16. As a new article of manufacture, a tanned leather having fixed upon its fibers a .mixture of oxides consisting of those of chromium and of a rare earth metal.

17. As a new article of manufacture, a tanned leather having fixed upon its fibers tanned leather having fixed upon lts fibers a the oxides of aluminum, chromlum and oft-a 'mixture of oxides, consisting of that of rare earth metal. 10

chromium and of a rare earth metal, andof In testimony whereof I hereunto aifix my 5 a mixture of soap, consisting of that of signature.

chromium and of a rare earth metal.

1.8. As a new article of manufacture, a FRIEDRICH WQWEBER. 

